Automatic acoustic control for public address systems and the like



AUTOMATIC ACOUSTIC CONTROL FOR PUBLIC Oct. 11, 1949. G. N. WETZEL 2,484362 ADDRESS SYSTEMS AND THE LIKE Filed Jan. 24, 1946 Com niacin PaWER 3 SUPPLY f4 1L 1 77 z l Voice FREQ LOUD.

SOURCE SPEAKER 7/ 6 Q I Y /7 GRA/WNWETZEL I INVENTOR.

Patented Oct. 11, 1949 AUTGMATIC "ACOUSTIC CON T-ROL-FOR PUB- LIC ADDRESS SYSTEMS AND THE LIKE .QG-ran Wet e wQed apids Iowa assimo to Collins .Radi'o Company, jQedar fiapidsllowa,

a corporationof Iowa ,Applicationalanuaryfi, 1946, Serial 643,161

.4 Claims.

s e ti n elates t ele trica 5591 6.1 qu nc r roduc n s temsans zmon part ula 1y to the regulation of the volume of a public d ess sys m orthe .-u i WihqlfiSPQ t the u cal o s lev i th icini yio t 19nd:

speaker. p

In p i a ess sy tems u ed he vic n t of i a l d e mach ne suc a i m hin hop thelike theaswsfi n is pro: duced by the mac es when inoperation maybe r at o eht a. a I o t e epr du ed sou immth pumi a les loudspeaker. I-n such cases, it is ,desirable,

Order h in li ibi t wil be i ured t t a m means in easin th a ou i e e o the loudspeaker ovutput proportion to the acoustic noise inthe enyironsjof thelondspeaker. I have found th tthi -can hea wmsl shedaummatically by using the electric power l-ine load c ren s the d erminin tee e in con rolling the acoustic output level of the loudspeaker.

Accordingly, t is a ob ec o h s in ent on t provide a u i a d es s tem and the like wherein the voice requenc out u :Q' a cloudspea and t li se s automatical n -eased a the acoustic noise leyel {the env rons pf the loudspeaker is increased.

It is also an object of this invention to provide an automatic acousticyolumelcontrol circuit for use n n ec io wit alpublicad res s stem wherein the acoustic output of the system bears a definite and predetermined relationship to the current inpower supply conductors which: supply power to electrically driven machineryin the vicinity of the publicaddresssystem.

It is a further object of this invention to provide an automatic acoustic volume controLpublic address arrangement wherein the volume of the reproduced sound is automatically adjusted in accordance with changes 'inthe load current of the power supply system which feeds electrical equipment to be operated in the vicinity of the public address system.

A feature of this invention is that the automatic acoustic volume control may be made to have any desired relation to the current in the power supply system, by means of a relay-controlled attenuator.

Another feature of this invention is that the automatic volume control is achieved by the use of a small number of components and is controlled by the current in the power line supplying electric energy to the system.

Other objects, features and advantages not particularly enumerated, will be apparent after 2 a consideration of the following detailed description andtheappended claims.

Thedrawing is a cir'cuit diagram showing one preferred embodimentof the invention.

Referring more particularly (to the drawing, conductors sandi -conveygenergy from a suitable source 3 of commercial alternating current power supply :to thearea' in which the loudspeaker of the publicaddress systemlis located. These conductors may supplyone or more electrically driven machines 4, 5 as well as supplying the power for the .public .address amplifier ,6 connected to any source of voice. frequency signals 1' Amplifier 5 maybe of any well-known. grid controlled vacuumtjube type. Ehe power "current transformer 8 is situated at some suitableplace-along one of the conductors .2. 'Ifhepriniaryfaof transformer 53 consists of .oneof theicond uctors I, Zhere-shown as conductor 2, coiled ,around the transformer core ll). The conductor 2' may 'be coiled for a pluralityof,aroundthe core 1-19. It will be understood that an well-known current transformer may be used .with its primary connected in series withone oftheconductors I, 2.

To prevent encessiy'e vvvoltage drop across the transformer,. it is necessarysto X have the primary with as low a series reactan'ce as possible. For this reason, the number of turns .on the primary of the, transformernshould =be.small.

,Ifhe output oftransforrnensecondary H is fed to ya rectifier .12 which maybe .ofany suitable type, such fort examplelasthewellfknown dry disc or copper oxidetype. The potentiometer resistor [3.se'rves as the load resistor 0f rectifier v .l 2. -.Condenser 1.4 is a nsinoothing condenser and removes the ripple from theoutput ofrectifier l2. The windingof alternating.currtentrelay l5 receives aportion of theoutput, ofrectifier I 2 in. accordance with the vsettingsof the [movable arm l6 along resistor 13'."

When the winding of relay I5 is deenergized, the contacts are in the positions illustrated and the amplifier 6 is connected to the loudspeaker I! through the attenuator network I8 comprising resistors I9, 20 and 2|. Attenuator I8 limits the acoustic output of the loudspeaker H and fixes it at a predetermined value, when relay I5 is deenergized. If desired, one or more of the resistors I9, 20, 2| may be manually adjustable. The inclusion of this attenuator or circuit with the loudspeaker is through the armatures 22, 23 and their respective back contacts 24, 25. When relay !5 is operated, the attenuator is removed from the circuit, and the wires 26, 21 are directly connected through armature 23 and front contact 2%,

When the load current in power lines I, 2 rises above a predetermined level, this rise in line current is sufiicient to operate the contacts of relay l5. Thereupon the attenuator i8 is eliminated from circuit and amplifier 6 is directly connected to speaker l1. The elimination of attenuator I 8 allows an increasedamount of energy to be fed to loudspeaker l1 whichincreases its acoustic output proportionately. volume output of the loudspeaker therefore is a function of the power load current supplied ,by lines I, 2 to the neighboring electrical machinery.

If adjustable contact arm I6 is initially-adjusted along resistor l3 and the connections are" completed through contacts '24'and 25 a predetermined amount of attenuation occurs in net- The acoustic tively connecting a voice frequency signal attenu-- ator in circuit between said amplifier and reproducer.

2. The method of operating a public address amplifier and reproducer system for use in the vicinity of noise producing machines electrically driven from power supply mains and whose noise level is'proportionate to the loadcurrent in said mains drawn by said machines, which comprises adjusting the level of the amplifier output in accordance with a predetermined load level current in said mains and automatically varying the level Work I8 and causes limitation of the acoustic volume output of loudspeaker l1. If the noise level increases, as is the casewhen line I--2 supplies a greater load current, the amount of current flowing through relay l5 increases to a value sufii-.

cient to operate relay l5 and thereby eliminate attenuator I8 from the'circuit as heretofore described. The acoustic volume output of loudspeaker l'l immediately increases thereby compensating for the increase in noise level.

The use of a single relay as above described allows operation of the loudspeaker attwo difierent volume outputs. The use of a series of such marginal relays and associated attenuators will afford operation of the loudspeaker at a series of different volume levels. The number of relays used in each case'is determined among other things by the probable noise level, and each relay will be marginally wound to respond successively to different values of line load current.

While there has been here described a preferred embodiment, it will be understood that various changes and modifications may be made therein without departing from the scope of the invention. Thus the invention is not limited to use with A. 0. supply mains but may be used with D. C. mains. In that event, the relay It may be connected directly in series with the line [-2 or, if desired, it may be shunted across a load resistor which is connected directly in series with the line |-2.

What is claimed is:

t 1. In a sound reproducing system, a Voice-irequency controlled amplifier, a sound reproducer supplied from said amplifier, alternating current supply mains for supplying operating power to electrically driven machines located in the vicinity of said reproducer, a current transformer connected in series with said mains, a rectifier and potentiometer combination connected across the output of said transformer, an electro-magnetic relay having its winding connected to said potenof the amplifier output in accordance with variations in said load current in said mains.

3. Ina sound reproducing system for use in the vicinity of power machines electrically driven from power current supply mains and whose noise producing level is proportionate to the load current in said mains drawn by said machines, said tiometer, said relay having contact sets for sele csystem having an amplifier, a sound reproducing device connected more output of said amplifier, aload current transformer the primar of which is in series with said power mains,- a rectifier connected in circuit with the secondary of said transformer, a variable resistor in parallel with a condenser connected to the output of said rectifier and across the secondary circuit'of said transformer, a relay connected across said variable resistor, an attenuator connected between said amplifier and said device and arranged to be switched into and out ofcircuit by said relay, said relay being responsive to-the magnitude of the rectified current in the output of said rectifier.

1 4. In a soundreproducing system for use in the vicinity of power machines electrically driven REFERENCES 1 'orrEn The following references areoi record in the Numbe'r' 1v Na'm'e 7 Date 2,179,928. ""Hagenhous Nov. 14, 1939 2,22,4,'678 I Hathaway"; Dec. 10, 1940. 2,346,504 Place I Apr. 11, 1944 2,382,848 Baumgartner Aug. 14, 1945 22,392,218

Anderson on ...Jan. 1, 1946 

